In addition to forest developments and treatments directed to paper manufacturing process for developing mechanical strength and other equally important properties, in the last few years, researchers of the sector have been working on additives association as the most promising means to enhance these properties in cellulose manufacturing process itself. Among the additives that have been used for manufacturing paper are the longer fibers, glues, dry and wet strength agents, starch, and others.
Document WO 00/28141 describes a method for treating lignocellulosic fibrous materials for enhancing the mechanical strength and humidity properties of the final product, which comprises fibrous materials, in which paper is the major example. The treatment involves the application of lignin derivatives in a solvent system with secondary additives which consist of a broad scope of sugars and natural polymers. This document describes the addition of additives in the paper machine approach flow, in the so-called wet end of the paper machine, where most additives are included in papermaking. Some additives mentioned in that patent application are widely known by the properties they provide when used in the recipe for producing some types (grades) of papers. In addition, the process described in that document requires the combination of the use of lignin for obtaining the desired results, which actually corresponds to the innovative aspect of that invention, and other secondary natural polymers are included as optional for boosting the development of the desired properties.
Another document describing the use of (the) biopolymer starch in a process for producing cellulose is PI9803764, which relates to a method for bleaching cellulose pulp with whitening chemical substances with the addition of starch, polyvinyl alcohols or enzymes. This document specifies the treatment for pulps having more than 5% lignin, emphasizing higher yield pulps such as mechanical pulps, thermomechanical pulps and chemothermomechanical pulps; thus, pulps without an ostensive bleaching process such as that of chemical pulps. The object of that invention is only to increase the whiteness of the pulp, and the secondary additives, such as enzymes and starch, are only intended to increase the efficacy of the optical whitening agents thus enhancing their absorption on the surface of the treated pulp fibers. These products for enhancing pulp whiteness are added in the last step before drying the pulp and do not develop the mechanical properties of the pulp.
Document US49267498 refers to a papermaking process where the additives are claimed as a retention aid. Therefore, this document teaches a polymer that must be added to the final cellulose pulp very close to the papermachine to keep a big formed floc and improve drainage. Examples 2 and 3 of this document mention a compozil additive, that is, a combination of two products to improve flocculation alone.
Document U.S. Pat. No. 4,756,801 teaches the addition of cationic starch in particular to the papermaking process to obtain a bonding agent in order to use different kinds of pulps and fillers in the paper production. The examples contained in this document again mentions additives as retention aids, which is its well known application for polymers in papermaking processes.
Document EP1080271 exclusively refers to a papermaking process and to the use of polysaccharides as a retention aid, where a secondary effect could be the strength. Besides, these polysaccharides must to have an aromatic hydrophobic group. This patent is also related to a minimum conductivity suspension. It is also the case of document EP0148647, which discloses a papermaking process. In the example 1, the application of polymer was carried out for softwood (long fibers) and starch was added just before the paper sheet formation. The result obtained in accordance to that example was retention of the pulp suspension during the paper sheet formation. Example 2 in turn mentions the combination of products in order to improve retention also using softwood as fiber furnish. Thus, this document refers to a polymer is used as additive to attach fines and fillers to form flocs and improve retention.
Document WO2004/046464 mentions the treatment of cellulosic material with clay and the secondary use of starch or other products as a retention aid. The main objective of this document is to produce cellulose with filler, were the secondary additives are only to become it possible.
In view of the above, it can be seen that it is already known for prior art to use polymers such as starch but as retention aids in the production of paper.
Accordingly, the object of the present invention is the use of a biopolymer during the process for producing cellulose pulp that is capable to promoting changes in the mechanical properties of the pulp as well as in other important properties, such as drainage, drying, porosity and pulp refining.